Nelson Pass F5 build, Part Trois...

[Russellc]

I have used the "Light bulb variac" when I built my P-P 6550 tube amp.
It worked very well. When first switched on, the lightbulb glowed brightly, then if all is well, dims down.....if not, it glows brighter. Worked like a charm, I had unintentionally reversed the leads from the outputs, which made the amp highly unstable. That, and the bias meters swinging wildly let me know
before anything went up in flames!

russellc

[westend]

Originally Posted by Russellc

Whoops, I see you have already been there and that advice may be in question, sounds like maybe they have it backwards? I have the daniels boards, so I need to find out....

Russellc

Russell,
I put a meter on the trimmers before installing them, like I do for most of the components. I didn't want any surprises about values and have the mission of sorting out a mislocation, etc.. I measured that they were at the highest resistance. After placing them in circuit and prior to start-up, I metered them again and second guessed myself into believing I had them set wrong. A lot of this confusion was reading stuff that is passed along in the original DIY thread.

Here is a copy of the Datasheet of the 3296 Bourns trimmer which was supplied by Tech-DIY. NP commented that there is no difference in the method of mounting but I followed SpecialI's and Tal's orientation.

I am posting this up here so others don't get confused and have that heart-stopping moment when the amp is fed full current.

[specialidiot]

Originally Posted by westend

Russell,
I put a meter on the trimmers before installing them, like I do for most of the components. I didn't want any surprises about values and have the mission of sorting out a mislocation, etc..

I triple measured every resistor before soldering them in place. Although I was an electronic tech doing board level troubleshooting in a previous life, I have learned that I no longer have the patience, or the knack for it.

You'll find that the pots are three-legged, with the resistance between the opposite legs the total value of the pot. Turning the screw varies the resistance between the center leg and the outside ones (duh). You'll find that two adjoining pads that the legs solder to are shorted at the pcb level. So you just have to figure that the value that matters is between the other two pads.

Yeah, clear as mud right?

Lance if you decide to go with an engraver to do an F5 logo, please let me know. I'd do mine as well.

It sure sounds nice tonight, how about yours?

[westend]

Originally Posted by specialidiot

I triple measured every resistor before soldering them in place. Although I was an electronic tech doing board level troubleshooting in a previous life, I have learned that I no longer have the patience, or the knack for it.

You'll find that the pots are three-legged, with the resistance between the opposite legs the total value of the pot. Turning the screw varies the resistance between the center leg and the outside ones (duh). You'll find that two adjoining pads that the legs solder to are shorted at the pcb level. So you just have to figure that the value that matters is between the other two pads.

Yeah, clear as mud right?

Lance if you decide to go with an engraver to do an F5 logo, please let me know. I'd do mine as well.

It sure sounds nice tonight, how about yours?

Jeff, I'm definitely thinking about the etching, machining, laser of an "F5" into the faceplate. It my hunt bears fruit, I'll let you know and we can double up. I haven't had time to hook it up, lol, been too busy metal working.

Old Fragger kinda' reminded me I should get busy on the faceplate so I'll show how far I got tonight. I could probably have had it to a mirror finish except for lack of sandpaper. I bossed the mounting bolt holes, chamfered all the holes on the drill press, and cut the edge chamfer on the router table. The handles will be cut down to match the faceplate height. I had to include a pic of the router table (I'm just really pleased how that turned out). It has saved a lot of time around here.

I promise I'll set up the F5, tomorrow, and report back what my impressions are *practices glowing adjectives in sleep*.

[thefragger]

Very nice looking! I tend to paint all my stuff, it's just easier

Almost there!

If the faceplate is aluminum, maybe you could find a local (read: small) cabinetmaker or sign manufacturer with a CNC getup to mill out what you want?

[westend]

Originally Posted by thefragger

Very nice looking! I tend to paint all my stuff, it's just easier

Almost there!

If the faceplate is aluminum, maybe you could find a local (read: small) cabinetmaker or sign manufacturer with a CNC getup to mill out what you want?

I was thinking about painting almost all of the chassis pieces but after you get done sanding and cleaning, you still need to use an acid etching primer and then sand, paint, sand, paint, and probably a third coat, sand, paint, and finish wet sand. I added it all up and it seemed easier to just sand and polish. I guess if I want the aluminum tarnish-free, I'll have to anodize it or cover it with laquer. I could skip all that and take it to Jeff's powder-coating people but where's the fun in that?

The etching or machining is kind of a sticking point. None of the places that use a CNC setup want to break their rhythm to take on a little deal like this. They want to punch out as many parts as possible to make the machine earn it's keep. I do have "one card to play" and I'm weighing the choice of playing it.

[thefragger]

Yea... it can be tough to find a small shop with the gear and the ability to do a one-off. A neighbour of mine runs a custom cabinetry business (his garage is a thing of beauty) and he's usually busy, but has no problems doing one-off deals when he gets slow.

I'd say ask around and try to figure out when slow-season is (there always is one), then approach them in that window to see if they'll do it for yah. You may be waiting a while, though.

[Russellc]

Originally Posted by specialidiot

I triple measured every resistor before soldering them in place. Although I was an electronic tech doing board level troubleshooting in a previous life, I have learned that I no longer have the patience, or the knack for it.

You'll find that the pots are three-legged, with the resistance between the opposite legs the total value of the pot. Turning the screw varies the resistance between the center leg and the outside ones (duh). You'll find that two adjoining pads that the legs solder to are shorted at the pcb level. So you just have to figure that the value that matters is between the other two pads.

Yeah, clear as mud right?

Lance if you decide to go with an engraver to do an F5 logo, please let me know. I'd do mine as well.

It sure sounds nice tonight, how about yours?

Making it even muddier, I have the daniels boards, and apparently some believe there is a difference in that hookup between the daniels board and cviller boards. I guess I should ask Peter for clarification on this. I'm going to (eventually) fire up with my variac, so I should have slightly more warning if something is a miss.

Russellc

[Russellc]

Got a response over on DIY from Peter. He said as far as he remembered,
clockwise reduced the bias. He said he fires them up with the pot in its half way position, and has no trouble.

Russellc

[golana]

There are companies on line that do this etch/ingraving all day long. I know about this from guitar amps face plates. Shipping a simple plate back and forth should be relatively cheap. Here's one, I'll just need to keep my eyes open for a few nights. http://www.amplates.com/faceplates.html

[MrIgotNomoney]

Guys
Good info about the pot orientation, I have got my boards and and I am starting to plan out my build.
The biggest hassle is getting heatsinks and a chassis together, Im thinking to save money the best bet is to build my own chassis. Im still reeling over the cost and shipping for a pair of Conrad heatsinks.
I have a bunch of Nichicon 10000uf@50v I was thinking about using 10k uf and going with a 600va transformer for the ps. anyone using CVillers rectifier boards ?
The small parts and silicon, are pretty reasonable from TechDiy

bob

[specialidiot]

Originally Posted by MrIgotNomoney

The biggest hassle is getting heatsinks and a chassis together, Im thinking to save money the best bet is to build my own chassis. Im still reeling over the cost and shipping for a pair of Conrad heatsinks.

I like squidward's idea of repurposing an old amp chassis and heatsinks. It would have to be a pretty big one - for the heatsinks anyway.

anyone using CVillers rectifier boards ?

In an earlier discussion which might even be in this thread, some of us agreed that buying a block rectifier for a few bucks is well worth it compared to having to assemble multiple parts. You may save a buck or two, but the opportunity for failure is greater and its far less work to use the block.

[MrIgotNomoney]

Specialidiot
I was thinking the same thing, the boards make for quite a few failure areas. I loke the block rectifiers reliable and easy to mount. Can use push on terminals too.
Cheeper after you figure in the diodes and heatsinks.
bob

[cbrworm]

I can verify the Pdaniels boards clockwise lowers bias, CC raises bias.

Either way, when I fired mine up the first time I had voltmeters on both .47 ohm resistors and used a 100 watt bulb in series. They should start out as 0 volts with no bias and increase to .590ish as you turn the pots counter clockwise. I removed the bulb once I saw the bias come up to about .100 on both sides successfully

[Squidward]

Ebay seller johnango is the guy who runs Antek, the torroid transformer place. Looks like he's also selling heatsinks for cheap now, too. Might be worth checking it out.